Clear monolayer label filmstock

ABSTRACT

PCT No. PCT/US96/15291 Sec. 371 Date Feb. 12, 1998 Sec. 102(e) Date Feb. 12, 1998 PCT Filed Sep. 24, 1996A monolayer or multilayer label filmstock having low haze while maintaining sufficient stiffness and die-cuttability to be used in a deformable, pressure-sensitive label. The low haze allows the deformable labels to be substantially clear. The label filmstock comprises a polymer blend of a polyolefin and a glassy polymer.

This application claims benefit of U.S. Provisional Application No.60/004,334, filed Sep. 26, 1995, now abandoned.

This invention relates to polymer resin blends generally, and morespecifically but without limitation to resin blends useful for makingfilm capable of being made into labels (that is, label filmstock) suchas deformable, pressure-sensitive labels. This invention also relates tolabels generally, and more specifically but without limitation todeformable, pressure-sensitive labels and to label filmstock for makingsuch labels.

It is well known in the art to use thermoplastic label filmstock formaking labels that are preferable in many respects to paper labels.Deformable thermoplastic labels desirably are resistant to moisture,tearing, cracking, creasing, wrinkling, shrinking, etc. These propertiesare especially important when the labels are applied to squeezable orotherwise deformable substrates.

For making labels, label filmstock is generally used in conjunction withan adhesive layer for adhering the label filmstock to a selectedsubstrate. The adhesive is generally selected so that when the labelfilmstock is adhered to the substrate, the strength of the labelfilmstock-adhesive interface, the strength of the substrate-adhesiveinterface, and the cohesive strength of the adhesive itself are allgreater than the forces required for deformation and recovery of thelabel filmstock. The adhesive should be sufficient to enable the labelto accomplish its intended purpose for the reasonable lifetime of adeformable container. Pressures sensitive adhesives are preferable andinclude the acrylic and styrene-butadiene adhesives.

For making labels, label filmstock is also generally used in conjunctionwith a release liner. The release liner is releasably bonded to theadhesive until the label filmstock/adhesive is suitably peeled away fromor dispensed from the liner and adhered to a flexible or deformablesubstrate. The release liner may be any suitable conventionally knownliner material for labeling applications.

In order to be successfully used as label filmstock for deformable,pressure-sensitive labels, a film should also meet three additionalgeneral requirements: good optics, die-cuttability, and appropriatestiffness. Whether a label filmstock has good optics is applicationdependent. In some cases, a low haze high gloss film is required. Inother cases, a higher haze, lower gloss film is required. For example,blow molded high density polyethylene bottles may have a 60 degree glossfrom 19-36 percent, as measured by ASTM D 2457, while some polypropyleneblow molded bottles may have a 60 degree gloss up to 80 percent.

In terms of die-cuttability, a film/adhesive/release liner compositedesirably should be die-cuttable on a rotary die at commercialmanufacturing speeds without web breaks or damage to the liner. When afilm is not very die-cuttable, then more sophisticated and expensiverelease liners must be used.

In terms of stiffness, a label filmstock must be sufficiently stiff todispense easily from a release liner, but not too stiff that it wrinklesor deforms when applied to a deformable container.

Polystyrene-based label filmstocks are generally sufficientlydie-cuttable and stiff. The stiffness of these polystyrene-based labelfilmstocks allows for good machine processability in label applicationequipment, but limits their utility on deformable substrates becauselabels made from these polystyrene-based label filmstocks wrinkle whenapplied to a deformable substrate.

U.S. Pat. No. 5,151,309 issued to Dollinger ("Dollinger") discloses alabel filmstock comprising a polystyrene blend. The label filmstock ofDollinger is die-cuttable and has good stiffness. However, the labelfilmstock of Dollinger has very high haze due to the polystyrene blendcomponent. This high haze precludes the use of Dollinger label filmstockin clear labels.

Polyethylene label filmstocks, such as disclosed in Re. 32,929 issued toEwing ("Ewing"), can be formulated to meet a range of optical andstiffness requirements, but are difficult to die-cut and to dispensefrom a release liner in labeling equipment because of their elongationand yield characteristics. Fillers may be added to polyethylene labelfilmstocks to control die-cuttability, but the addition of fillerslimits the optical properties possible. Highly oriented polyethylenelabel filmstocks have improved die-cuttability but have deficiencies dueto the optical properties obtainable as well as excessive stiffness. Afilmstock having excessive stiffness is generally unable to besuccessfully utilized in a deformable label (that is, a label to beadhered to a deformable substrate).

The present invention provides label filmstock having an improvedcombination of optics, die-cuttability, and stiffness. In one aspect,the present invention provides a label filmstock having low haze whilemaintaining sufficient stiffness and die-cuttability to be used in adeformable, pressure-sensitive label. This low haze allows labelfilmstock of the present invention to be made into labels for deformablesubstrates that are substantially clear.

Label filmstock of the present invention may be a monolayer or amultilayer film. Preferably, label filmstock of the present invention isa monolayer film. In any case, at least one layer (or the only layer ina monolayer film) of the present invention comprises a polymer blend ofa polyolefin and glassy polymer. The polyolefin is the most prevalentcomponent in film labelstock of the present invention and generallycomprises at least about 50 weight percent of the label filmstock.Preferred polyolefins include copolymers of ethylene and octene andblends of low density polyethylene ("LDPE") and high densitypolyethylene ("HDPE"). Generally, the glassy polymer does not comprisemore than about 50 weight percent of the label filmstock, andpreferably, does not comprise more than about 25 weight percent of thelabel filmstock. Preferred glassy polymers include poly(methylmethacrylate) ("PMMA") and styrene-acrylonitrile polymer ("SAN").

Label filmstock of the present invention optionally may contain othermaterials in addition to the polyolefin and glassy polymer components,so long as these other materials in the amounts contemplated do notunduly interfere with achieving the desired combination of optics,stiffness, and die-cuttability. These optional materials includepigments, such as titanium dioxide; compatibilizers; andprintability-enhancing polymers, such as copolymers of ethylene andacrylic acid ("EAA").

The present invention provides label filmstock having reduced haze whilemaintaining sufficient stiffness and die-cuttability to be used indeformable, pressure-sensitive labels. Stiffness of label filmstock ofthe present invention was determined by measuring the machine direction1 percent secant modulus using ASTM D 882. Generally, label filmstock ofthe present invention should have a machine direction 1 percent secantmodulus of less than about 100,000. Preferably, label filmstock of thepresent invention will have a machine direction 1 percent secant modulusof about 50,000.

It should be noted that the stiffness of label filmstock in general canbe increased by increasing the thickness of the filmstock. However,label filmstock of the present invention is generally no more than about5 mils thick, and preferably no more than about 4 mils thick. Labelfilmstock of the present invention is generally at least about 2 milsthick, and preferably at least about 3 mils thick.

Determining whether label filmstock exhibits sufficient die-cuttabilityis somewhat subjective in nature. Generally, this determination is madeby incorporating the filmstock into a filmstock/adhesive/release linercomposite structure by methods well known in the art and die-cutting thecomposite structure on a rotary die at commercial manufacturing speedsto see if there are web breaks or damage to the release liner. However,a lower ultimate elongation of the label filmstock is believed to be anindication of enhanced die-cuttability of a filmstock/adhesive/releaseliner composite structure. Machine direction ultimate elongation forlabel filmstock of the present invention was measured by ASTM D 882.Generally, label filmstock of the present invention will exhibit anultimate elongation of less than about 400 percent.

The haze of films of the present invention was measured using ASTM D1003. The haze level needed in label filmstock of the present inventiondepends on the particular application. However, it is a feature of thepresent invention that when compared to known label filmstock, labelfilmstock of the present invention can be produced that exhibits lowerhaze while maintaining substantially similar stiffness anddie-cuttability. This lower haze allows label filmstock of the presentinvention to be made into substantially clear labels for deformablesubstrates. To prepare substantially clear labels from label filmstock,the label filmstock should exhibit a haze value of less than about 60percent, and preferably, about 50 percent or less.

Generally, label filmstock of the present invention comprises a blend ofat least one polyolefin and a glassy polymer. The exact amount of eachcomponent will vary somewhat depending on the desired characteristics ofthe resulting label filmstock. For example, the amount of glassy polymerpresent can be adjusted depending on the haze level desired. Generally,adding more glassy polymer will increase the haze level and lowering theamount of glassy polymer present will lower the resulting haze level.Also, the amount of glassy polymer needed to produce a particular hazelevel will vary depending on the particular type of glassy polymerutilized. However, the amounts of the components needed to produce anembodiment of the present invention can be discerned from the teachingsherein without undue experimentation. For the purposes of thisapplication all percentage amounts disclosed will be weight percentagesunless stated otherwise.

These polymer blends can be used to produce either monolayer ormultilayer filmstock using techniques well known in the art. Preferably,label filmstock of the present invention is a monolayer film. However,the present invention contemplates a multilayer label filmstockcomprising at least one layer having the same composition as would amonolayer label filmstock of the present invention.

The predominant component in polymer blends useful in producing labelfilmstock of the present invention is one or more polyolefins.Accordingly, the polyolefin component generally comprises at least about50 percent of the label filmstock.

The kinds of polyolefins useful in making label filmstock of the presentinvention are generally known in the art and include polyethylenes;polypropylenes; and copolymers of ethylene and octene, propylene,acrylate monomers, vinyl acetate, acrylic acid, methyacrylic acid,ionomers of acrylic acid, or ionomers of methyacrylic acid; and mixturesthereof.

A preferred polyolefin to be used in label filmstock of the presentinvention is a copolymer of ethylene and octene. One such copolymer isDOWLEX 2247 (available from The Dow Chemical Company). DOWLEX 2247 has amelt index of 2.7 and a density of 0.917 g/cc. Another preferredpolyolefin to be used in label filmstock of the present invention is ablend of low density polyethylene ("LDPE") and high density polyethylene("HDPE"). Additionally, including small amounts (that is, generally notmore than about 10 weight percent) of a copolymer of ethylene andacrylic acid ("EAA") tends to enhance the printability of the labelfilmstock. An example of such an EAA copolymer is Primacor 1410(available from The Dow Chemical Company).

Label filmstock of the present invention also contains a glassy polymer.For purposes of this application, a glassy polymer is a polymer having aglass transition temperature greater than the temperature at which theresulting label filmstock will be used. When incorporated into labels, acomposite label filmstock/adhesive/release liner structure willtypically undergo a die-cutting operation at approximately 100° F.(37.8° C.). Accordingly, glassy polymers useful in the present inventionwill typically have a glass transition temperature greater than about100° F. (37.8° C.).

Glassy polymers preferred for use in the present invention includepoly(methyl methacrylate) ("PMMA") and styrene-acrylonitrile polymer("SAN"). PMMA is generally more preferred than SAN. The precise amountof glassy polymer utilized in label filmstock of the present inventiondepends on the particular glassy polymer utilized and the combination ofoptics, stiffness, and die-cuttability desired.

As the weight percent of glassy polymer in a filmstock decreases, themachine direction ultimate elongation of the filmstock increases. Labelfilmstock having lower ultimate elongation is usually more die-cuttablethan label filmstock having higher ultimate elongation. Generally, labelfilmstock of the present invention will exhibit a machine directionultimate elongation of less than about 400 percent as measured by ASTM D882. Label filmstock should ultimately be tested for die-cuttability oncommercial equipment at commercial manufacturing speeds.

Also, as the amount of glassy polymer present in filmstock increases,the 1 percent secant modulus of the filmstock increases. The amount ofglassy polymer present in filmstock of the present invention should notbe so much as to cause the 1 percent secant modulus to be greater thanabout 100,000. Generally, the amount of glassy polymer present in labelfilmstock of the present invention is less than 50 percent, andpreferably, less than 25 percent.

It should be noted that label filmstock of the present invention maycontain other materials in addition to the polyolefin and glassy polymercomponents, so long as these other materials in the amounts contemplateddo not unduly interfere with achieving the desired combination ofoptics, stiffness, and die-cuttability. For example, a conventionalpigment such as titanium dioxide may be added to the label filmstock.Generally, no more than about 10 percent by weight of titanium dioxideis needed to achieve a white label suitable for printing. However,greater amounts of titanium dioxide could be added so long as there isno undue interference with achieving the desired combination of optics,stiffness, and die-cuttability.

Additionally, a compatibilizer may be added to label filmstock of thepresent invention. If added to label filmstock of the present invention,compatibilizers generally will be present in amounts less than about 10weight percent. Although a compatibilizer is not a critical element ofthe present invention, the present invention contemplates that utilizinga compatibilizer could realize certain processing advantages, such asreduced die-face buildup during extrusion of label filmstock of thepresent invention.

EXAMPLES

Monolayer films were prepared using a cast film process. Each film was3.5 mils thick. Each film consisted of a blend of Dowlex 2247 and one offour glassy polymers. The four glassy polymers used were a generalpurpose polystyrene ("GPPS") (Styron 665, available from The DowChemical Company), a high impact polystyrene ("HIPS") (Styron 404,available from The Dow Chemical Company), a styrene acrylonitrile("SAN") (Tyril 990, available from The Dow Chemical Company), and apoly(methyl methacrylate) ("PMMA") (V920, available from Atohaas).

Films with various weight percentages of glassy polymer were tested forhaze via ASTM D 1003, machine direction 1 percent secant modulus viaASTM D 882, and machine direction ultimate elongation via ASTM D 882.Tables I-III show the results of these tests.

The film containing 0 weight percent glassy polymer and the filmcontaining 33 weight percent HIPS were further evaluated fordie-cuttability at a commercial die manufacturer (ROTO-DIE) afteradhesive coating and lamination to a release liner. The film containing0 weight percent glassy polymer (that is, ultimate elongation of 1000)was not die-cuttable, whereas the film containing 33 weight percent HIPSwas die-cuttable.

                                      TABLE I                                     __________________________________________________________________________    Haze (percent)                                                                Glassy                                                                            Weight Percent of Glassy Polymer                                          Polymer                                                                           0 percent                                                                          5 percent                                                                          10 percent                                                                         15 percent                                                                         20 percent                                                                         25 percent                                                                         33 percent                                  __________________________________________________________________________    HIPS                                                                              3                        98                                               GPPS                                                                              3    73        92        95                                               SAN 3    35        71        76   83                                          PMMA                                                                              3         22        41   48                                               __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    1 percent Secant Modulus (psi)                                                Glassy                                                                            Weight Percent of Glassy Polymer                                          Polymer                                                                           0 percent                                                                          5 percent                                                                          10 percent                                                                         15 percent                                                                         percent                                                                            25 percent                                                                         33 percent                                  __________________________________________________________________________    HIPS                               65,000                                     GPPS                                                                              15,800                                                                             21,000    32,100    54,000                                           SAN 15,800                                                                             25,700    51,600    77,700                                                                             102,500                                     PMMA                                                                              15,800    29,300    55,800                                                                             74,100                                           __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________    Ultimate Elongation (percent)                                                 Glassy                                                                            Weight Percent of Glassy Polymer                                          Polymer                                                                           0 percent                                                                          5 percent                                                                          10 percent                                                                         15 percent                                                                         20 percent                                                                         25 percent                                                                         33 percent                                  __________________________________________________________________________    HIPS                                                                              1,000                         450                                         GPPS                                                                              1,000                                                                                700     900       600                                              SAN 1,000                                                                              1,000     900       200  200                                         PMMA                                                                              1,000     1,000     200  150                                              __________________________________________________________________________

Monolayer films were prepared using a cast film process. Each film was3.5 mil thick. Three films consisted of 85 weight percent of a lowdensity polyethylene having a melt index of 1.9 and a density of 0.925g/cc (LDPE 535, available from The Dow Chemical Company) and 15 weightpercent of a glassy polymer. The glassy polymers utilized were GPPS(Styron 665), SAN (Tyril 990), and PMMA (V920). A fourth film consistedof 100 weight percent LDPE 535. Each film was tested for haze, machinedirection ultimate elongation, and 1 percent secant modulus. The resultscan be found in Table IV.

The 100 weight percent LDPE films appear to have good haze and ultimateelongation values. However, as taught in U.S. Pat. No. 5,151,309 issuedto Dollinger, polyethylene label filmstock is difficult to die cut andto dispense from a liner in labeling equipment.

                  TABLE IV                                                        ______________________________________                                                 Haze      Ultimate Elongation                                                                        1 percent Secant                              Glassy Polymer                                                                         (percent) (percent)    Modulus (psi)                                 ______________________________________                                        None      5        400          20,600                                        GPPS     80        220          59,600                                        SAN      78        200          62,900                                        PMMA     58        140          45,000                                        ______________________________________                                    

Two additional films were prepared using a cast film process. Each filmcontained 42 weight percent of low density polyethylene (LDPE 681,available from The Dow Chemical Company), 40 weight percent of highdensity polyethylene, HDPE 058620, available from The Dow ChemicalCompany), 10 weight percent of a glassy polymer, and 8 weight percent ofa copolymer of ethylene and acrylic acid (Primacor 1410, available fromThe Dow Chemical Company). The glassy polymer used in the first film(Film V-1) was a polystyrene (Styron 680, available from The DowChemical Company) and the glassy polymer used in the second film (FilmV-2) was PMMA (V-920, available from Atohaas). Film V-1 was 3.66 milsthick and Film V-2 was 3.73 mils thick. Each film was tested for machinedirection ultimate elongation, machine direction 1 percent secantmodulus, and haze.

                  TABLE V                                                         ______________________________________                                        Property Tested  Film V-1 Film V-2                                            ______________________________________                                        Elongation       282      176                                                 percent 1 Modulus                                                                              80,675   66,684                                              Haze             62.5     51.5                                                ______________________________________                                    

What is claimed is:
 1. A monolayer label filmstock, comprising:a)greater than about 50 percent by weight of a polyolefin component, saidpolyolefin component consisting essentially of a blend of high densitypolyethylene and low density polyethylene; b) no more than about 50percent of a glassy polymer; and c) no more than about 10 percent byweight of a copolymer of ethylene and acrylic acid.
 2. A deformablelabel suitable for attachment to a selected substrate, comprising:a) thelabel filmstock of claim 1; and b) an adhesive layer for adhering saidfilmstock to the selected substrate.
 3. A deformable label according toclaim 2, wherein said label filmstock exhibits a haze of less than 60percent as measured by ASTM D
 1003. 4. A deformable label according toclaim 2, wherein the glassy polymer is either a poly(methylmethacrylate) or a styrene-acrylonitrile polymer.
 5. A deformable labelaccording to claim 2, wherein said label filmstock further comprisestitanium dioxide.